Acoustic diaphragm



Dec. 4, 1928. 1,693,727

H. cs. PAPE ACOUSTIC DIAPHRAGM Filed April 15, 1926 INVENTOR Patented Dec. 4, 1928.

UNITED STATES PATENT OFFICE.

ACOUSTIC DIAPHRAGM.

Application filed April 15, 1826. Serial No. 102,291.

This invention relates to acoustic diaphragms and particularly'to the methodof deadening diaphragms and rendering them substantially non-vibratory, except under external stimuli. My invention relates further to diaphragm construction wherein a loading is provided, magnetic or otherwise, for forming a diaphragm capable only of a dead beat r In 'what follows the words dead heat refor 'to that manner of vibration whereby the article possessing the quality of dead heat vibrates only under external magnetic influence and will under conditions of practical use have substantiall no interfering or resonant frequency 0 its own. In other words, if the diaphragm having a dead beat is vibrated by a suddenly applied and momentary force, it vibrates only so long as the force thereon continues, and ceases to vibrate when the applied force ceases. Further, a dull or dead sound is emitted by the diaphragm if it is struck, the sound being only momentary and'setting up no sympathetic or interfering vibrations in the diaphragm. Such a diaphragm is operable to produce continuous sound only under continued stimulus and can roduce only the sound caused by the vibrations induced by said stimulus and no other. I

This invention is an improvement over that shown and described in my co-pending application, Serial No. 2,358,-filed January 14, 1925, for acoustic diaphragms, wherein I have shown a method of adding magnetic material, preferably in a. finely divided or comminuted state about the center of the diaphragm and in which I have also shown a diaphragm loaded with magnetic material near the center thereof. The present invention contemplates the provision of a method whereby the most efiicient magnetic loading for a diaphragm of any given thickness and for any given arrangement and shape of ma gnet poles for practical purposes may be predetermined and the loading added to the central part of the diaphragm in an eliicient and economical manner. The invention further contemplates the provision of a diaphragm to which a dead beat or a magnetic loading, or both, is efiiciently secured without detriment to the flexibility of the diaphragm.

The various objects of my invention will be clear from the description which follows and from the drawings, in which, Fig. 1 is a top plan view ofone form of improved diaphragm showing the type of loading resulting from the use of my improved method.

Fig. 2 is a vertical central section of the same.

Fig. 3 is a'top plan view of another form of loaded diaphragm.

Fig. is a vertical central section of the same.

5 is a similar view of a loading for the diap ragm in which magnetic material is eliminated, and

Fig. 6 is a top view showing one of the steps of m improved method.

It is we 1 known that if a thin diaphragm of magnetic material is arranged in the field of a sutliciently owerful magnet and particles of iron or siiicon steel or other magnetic material are dropped from a point above said diaphragm on to said diaphragm at points above the poles of the magnets influencing said diaphragm, the particles will arrange themselves along the shortest path of the magnetic lines of force produced by the magnet. I have discovered that if the diaphragm is then rotated about its center, even if over non-centrally arranged magnet poles, such as square faced or otherwise shaped holes, the particles of magnetic material arrange themselves in a pile or piles having a substantially circular base and varying in height, the height of the pile or piles being a maximum at the center thereof. Diaphragms loaded with such piles need not be placed in any specific position over the poles of a like mggnet, any position producing the same resu ts.

In order to determine the amount of material and the shape of the magnetic loading to be added to the conventional diaphragm disc, I contemplate among other methods, the application of enough gummy cementitious material to the center of the diaphragm as will hold together. the particles of magnetic material in a pile, and as will hold said pile securely to the diaphragm. The diaphragm, if desired, being placed in the magnetic field similar to those magnets with which it is to be used, said diaphragm or the magnets themselves are rotated until the particles arrange themselves in the cementitious material, which in this case is preferably gum rubber dissolved in a suitable solvent. Particles are added until rotation of the diaphragm in the magnetic field causes littleor no movement of said particles. The rotation may be continued until all of the particles on the diaphragm have come to rest, whereupon the rotation is stopped. It will be understood that it is the relative rotation of the diaphragm and the magnets which causes the formation of the ile in its peculiar shape. The particles sin in the gum rubber until some of them have reached a point near the bottom of the layer of rubber and all of said particles'have been cemented to ether by said rubber.

I have found t atwhen the above operation is performed, above oblong or squared pole pieces as 10 and 11, there results a plurality of piles of'a mixture of rubber and magnetic material consisting of a primary pile 12 having a circular base 13 at the center and a secondary pile 14 in the form of an annular ring outside of the primary pile, there being left an annular space as 15 substantially free of magnetic material. I believe that the secondary rin or pile 14 is formed by eddy lines of orce radiating from the outer portions 16 of the magnets (Fig. 6).

I contemplate the prevention of the formation of the secondary pile 14, when desired, as for instance, by the application of the gum rubber adhesive to a predetermined area. within the range of the primary pile only, or b otherwise preventing the permanent ad esion of the magnetic particles to the diaphragm at the points where the secondary pile would form. This may be done in various ways, as by covering that part of the diaphragm in a suitable manner such as by a tool or ring of the proper shape and size, and then removing said tool or ring, whereby the particles that would tend to .form said secondary pile are prevented'from forming; or, wherewith they are removed after the s'econda pile has been formed. After the coat 17 o gum rubber or pile 18 of combined rubber and magnetic material has been formed, whether in the shapes shown in any of the figures, or in any other shape found to be desirable, the solvent of the gum rubber is allowed to evaporate, with the result that there is left remaining a central substantially circular pile of magnetic ,material, or gum rubber, or both, highest at the center 19 of the primary pile. The particles, if any are present, are bound together by a flexible binder which deadens the natural frequency period of vibration of the diaphragm 20 so that the loaded diaphragm is responsive only to external magnetic influence and not to, anyvibration eriod of its own; that is, the diaphragm as a dead beat and may be called a dead heat diaphragm. lVhere no magnetic loading is desired, the magnetic material may be entirely omitted and the pile may be formed of gum rubber only, (Fig. 5) concentrated at the center of the diaphragm or said gum rubber may be spread as an even coat over one or both sides of said diaphragm. In the latter case, the rubber coating displaces the enamel ordinarily used to protect the diaphragm against corrosion. lVhen the shape, and size of the pile have been the method above descri d, it is obvious that similar diaphragms may be loaded with similar piles as by the use of suitable well known tools or depositors for depositing a predetermined amount of freely fiowin material in a predetermined shape on a predetermined area in a pile of predetermined hei ht. Such tools are well known, and may similar for instance to those used in the confectioners art for depositing sugars, ices and cream on pastry and need nothere be described in detail, as it will be understood that droppers of various kinds arealready in use for similar purposes, orthe loading of the diaphragm may be accomplished by the preformation of piles of proper area, shape and altitude by means of suitable molds from a mixture of gum rubber and finely divided particles of magnetic material. Said last-mentioned preformed piles may be secured to the diaphragm as by cementing said pile thereto by means of a thin coating of gum rubber dissolved in a solvent or as may be found most practical and expedient. For instance, the pile may first formed on a thin sheet, such as onion skin paper of extremely thin textuie, and the sheet may then be cemented to the diaphragm.

I prefer to use gum. rubber for the binder and for cementing the pile and the iii-.ignet-ic particles to the diaphragm for the reason that gum rubber is of such flexibility that it not only eliminates the possibility of interference with the function of the diaphragm, such as that caused by extraneous undesirable natural vibrations of the diaphragm itself not directly caused by the magnets, but because of the flexibility and resilience of that material the flexibility of the diaphragm is not materially affected, even though the thickness thereof may be increased by the loading.

In order to make the magnetic loading more effective, it is desirable to remove the enamel from the diaphragm at the area where the loading from the magnetic poles is made as small as possible. The gum rubber in the pile serves sufliciently as a protector,

pi'edetermined as by and enamel is, therefore, not needed over the area where the rubber is present.

It will bev seen that I have provided an im-. proved method for predetermining the size and shape of a magnetic loading and for forming adiaphragm loaded with such a loading, that the diaphragm produced by said methods is a dead beat diaphragm,

.and that said diaphragm may be arranged in any position in the proper plane over the m'agnetflpoles, all positions in said plane being equ ly effective.

Various changes in the process and in the diaphragms shown and-described are con-. templated falling within the scope of the appended claims, and it is not, therefore, intended that I be limited to thespecific method and construction set forth herein.

I claim:

1. The method of determining the shape and size of a diaphragm loading for-a given type of magnet poles comprising dropping particles of magnetic material on said diaphragm and relatively rotating said diaphragm and said poles while said diaphragm Y is in the magnetic field of said poles.

2. The method of determining the shape and size of a diaphragm loading for a given type of magnet poles comprising loading said diaphragm witi particles of magnetic material comparatively free to move on said diaphragm, and relatively rotating said diaphragm and said magnet poles while said diaphragm is arranged in the plane of its operative posit-ion with relation to said poles.-

3. The method of predetermining the characteristics of a magnetic loading on a diaphragm comprising the arrangement of magnet poles and a diaphragm loaded with movable magnetic material in their relative operative positions, and relatively rotating said diaphra m and said poles about the axis of said diaphragm while maintaining said diaphragm 1n the plane of its operative position.

4. The method of predetermining the size and shape of a magnetic loading for an acoustic magnetic diaphragm in a given magnetic field comprising the relative rotation of said diaphragm and said field about the axis of said diaphragm and dropping particles of magnetic material on said diaphragm at the center thereof, while covering said diaphragm at the area where a second pile would e formed.

5. Inan acoustic magnetic diaphragm, a loading comprising a pile of material, said pile being of varying hei ht, having a substantially circular base and having its greatest height at the center thereof,sa-id material being superimposed on and arranged at the center of said diaphragm, and including gum rubber.

6. In an acoustic magnetic diaphragm a magnetic loading'comprising a substantially conical pile of magnetic material at the center thereof and a secondary pile of less height than said primary pile concentric with and spaced from said primary pile.

7. In an acoustic diaphragm, a magnetic loading comprising a plurality of concentric piles of finely divided magnetic material superimpose'd on the diaphragm.

8. In an acoustic diaphragm, a plurality of piles of finely divided magnetic material arranged concentrically about and superimposed on the center of said diaphragm and a gum rubber binder for said piles securing said piles to said diaphragm and securing saidarticles in said piles. v

9.- an acoustic diaphragm, a centrally arranged pile having a circular base, a height greatest at the center and least at said base,

particles of magnetic material and gum rubher in said pile, and a second annular'pile including the same material assaid central pile, of less height than and arranged con cent-rically with and in spaced relation to said central pile.

10. In an acoustic diaphragm, a magnetic loading superimposed on the diaphragm comprisin finely divided magnetic particles arrange substantially in the form of a cone with the top of said cone rounded and a gum rubber binder for said articles.

11. The method of orniing loadings for diaphragms comprising the predetermination of the characteristics of the loadin for a given magnetic field by rotating a diap agm in said field about the axis of said diaphragm and dropping finely divided particles'of magnetic material on said diaphragm near the center thereof, forming piles of a mixture of magnetic material and dissolved gum rubber, having the same characteristics as the pile so predetermined, and securing said piles to the central portion of diaphragms.

12. In connection with a loaded magnetic diaphragmconstituting an actuated means and a given type of magnet poles constituting an actuating means, the method of de termining the shape and site of a loading for said actuated means for use with a given type of actuating means comprising the loading of said actuated means with particles of magnetic material comparatively free to move on said actuated means, whilein operative relation to said actuating means, and rotating at least one of said means.

13. In connection with a magnetiediaphragm constituting an actuated member and an electrically operated actuating member the method of predetermining the characteristics of a magnetic loadin for such an actuated member comprising t e arrangement of said actuating and actuated members in their operative relation, loading said actuated memher with movable magnetic material, and rotating one of said members while maintaining the operative relation of said members.

14. In connection with an acoustic diaticles of magnetic material are concentrated phragm constituting an actuated member the in a pile at the central portion of said actumethod of predet'ermining the'size and shape ated member and covering said actuated 10 of a. magnetic loading for such an actuatedv member to prevent the formation of a sec 6 member in the field of a magnet constituting ondary pile on said actuated member.

an actuating member, comprising rotating one of said members about its axis while par- HERMAN G. PAPE. 

